1. Field of the Invention
The present invention relates to a thermostat that controls coolant flow of an internal combustion engine, and more particularly to a thermostat and water pump in an integrated housing.
2. Description of the Prior Art
Although traditionally thermostats were mounted at the outlet of engines, recently they are being mounted on a coolant inlet side of the engine. The coolant flows through a water jacket (not shown) of the engine block 3. For medium to large size engines, as shown in FIGS. 1A and 1B, a thermostat 7 is placed upstream and adjacent the inlet of a water pump ensuring a relatively larger flow of coolant into the bypass passage 6 when the thermostat 7 is closed. A cooling system 1 causes the flow to be directed through a radiator 2 when the engine 3 is warmed up.
U.S. Pat. No. 4,938,185 granted to Doke, incorporated herein by reference, discloses a one-piece structure that includes a coolant pump and a thermostat. As shown in FIG. 2, this conventional engine cooling arrangement 10 includes a water pump 12 whose impeller 12a is rotatably housed in an impeller chamber 14. The impeller chamber 14 is formed in an impeller chamber section 16A integral with and forming part of a timing (front) cover 16. The water pump impeller 12a is driven through a pulley and belt drive. The timing cover 16 is mounted to the front face F of the cylinder block B, and covers a rotation transmission mechanism (not shown). In an inlet passageway section 16B of the timing cover 16, a coolant inlet passageway 18 leads to the inlet 14a of the impeller chamber. A thermostat 20 thermally controls the flow of the cooling water from the radiator to the water jacket of the cylinder block. The thermostat 20 has a heat sensor section 20a disposed in the inlet passageway 18. A coolant passageway 22 allows coolant from the radiator to flow to the inlet passageway 18 when a valve section 20b of the thermostat 20 opens. Another coolant passageway 24 from a heater and a bypass passageway 26 from the water jacket of the cylinder block are each directly connected to the inlet passageway 18. A coolant outlet passageway 28 connects an outlet 14b of the pump impeller to the cylinder block B, passageway 28 being part of outlet section 16C of the timing cover 16.
The operation of the conventional cooling arrangement will now be described. Coolant from the radiator is suppliable through the thermostat valve section 20b into the inlet passageway 18 and thereafter sucked into the pump impeller chamber 14. The coolant discharged from the water pump 12 is recirculated through the outlet passageway 28 to the water jacket of the cylinder block B. Coolant discharged from the water jacket is fed to the radiator and the heater. When the engine is cold, coolant discharged from the water jacket is recirculated to the inlet passageway 18 bypassing the radiator in order to assist warm-up of the engine. The inlet passageway 18 is formed straight to enable the engine cooling arrangement to be easily produced by die-casting.
FIG. 3 illustrates a conventional thermostat, where a frame 37 having a flange 32 secures the components of a thermostat 30, so that a main valve 33 is held by a spring 35 and a bypass valve 39 is held by a spring 38. A wax element 36 is secured to the frame 37 by a stop ring 34. The wax element 36 drives a piston 31 with a lift amount of the piston 31 being proportional to the temperature sensed by the wax element 36.
The conventional cooling arrangement does not respond quickly to the change in temperature of the coolant as the engine warms up and does not mix bypass flow (hot coolant) with cold coolant from the radiator. Hysteresis and overshoot result from the coolant temperature changing when flowing through the cylinder block after the valve action of the thermostat, and a lack of stability results.
U.S. Pat. No. 5,503,118 granted to Hollis discloses a temperature control system having a water pump in a housing with flow restrictor valves. The electronically controlled restrictor valves are kept closed to retain the coolant in the cylinder head, and are then activated when the engine has sufficiently warmed-up in order to permit coolant flow into the engine block. The valves are controlled by a computer so as to maintain the sensed oil temperature at an optimum value.
U.S. Pat. No. 5,715,776 granted to Seidl discloses a cooling system having a water pump, and a thermostat for selecting the coolant flow to either a radiator or the water pump. The flow path of the circulating coolant forms a particular pattern through the cylinder block that depends upon the temperature being either below or above the thermostat""s predetermined opening point.
U.S. Pat. No. 5,113,807 granted to Kobayashi discloses a thermostat and cooling pump assembly arranged at a side position of an engine for communicating a heat exchanger with the engine cooling jacket. The thermostat is positioned between ends of the engine and adjacent the heat exchanger.
U.S. Pat. No. 5,216,984 granted to Shimano et al. discloses a thermostat housing provided integrally in an end portion of one of the cylinder heads that is bounded by the water pump. The water pump has a sprocket that is driven by the timing chain.
U.S. Pat. No. 4,662,320 granted to Moriya discloses a water pump directly coupled to the engine""s cam shaft.
U.S. Pat. No. 5,992,755 granted to Kuse discloses a thermostat that has a pressure equalizing hole in its flange, and increases the lift-up rate at low temperature by reducing a return spring constant and reducing a seal spool thickness. Also, a higher lift increasing rate results in an increase in coolant flow rate and a lowering of upper limit coolant temperature. The thermostat seeks to decrease the upper limit temperature of the coolant.
U.S. Pat. No. 5,970,927 granted to Suzuki discloses an apparatus for circulating cooling water to an engine body, a radiator, a heater core, and an oil cooler. A connecting point, between the oil cooler cooling water communicating passageway and the heater core cooling water passageway, is located upstream of a thermostat-type flow control valve. A second thermostat-type flow control valve is located adjacent a radiator and operates at a significantly lower temperature. The configuration and action of the various flow control valves allows the heater core to remain unaffected by the flow of cooling water through the oil cooler.
The conventional cooling arrangements do not respond quickly to the change in temperature of the coolant as the engine warms up and do not mix bypass flow (hot coolant) with cold coolant from the radiator. The conventional activation of thermostats only indirectly controls coolant valves after the coolant has passed through separate passageways and through an engine. A disparity between the hot and cold coolant temperatures causes abrupt reaction to sudden temperature differentials that can result. Hysteresis and overshoot result from the coolant temperature changing when flowing through the cylinder block after the valve action of the thermostat, and a lack of stability results.
The present invention provides a thermostat, system, and method for achieving an improved control of cooling in an internal combustion engine. Mounting the thermostat at the inlet side of an internal combustion engine ensures a relatively larger flow of coolant into the bypass and enables reduction of the range of coolant temperature distributions in the water jacket when the thermostat valve is closed.
A significant advantage is obtained by stabilizing coolant temperatures. It is an object of the present invention to provide a minimum of overshoot and hunting by a thermostat that acts to stabilize the coolant temperature by opening and closing. Another object of the invention is an improved temperature control of an air conditioning system. A further object of the invention is a reduced hysteresis in a thermostat""s controlling action. A still further object of the invention is an improved radiating efficiency of a radiator.
To achieve these objects, a thermostat according to the present invention controls coolant flow of an internal combustion engine, the thermostat arranged in a housing where coolant from the radiator and from the bypass passage are mixed so as to control flow of the coolant from both passages by the use of valve means. The thermostat is assembled in a water pump case in order to integrate the parts into a single structure. A heat-responding element of the thermostat device and a valve body are individually arranged adjacent the water pump impeller. The heat responding element of the thermostat device is arranged downstream of the water pump impeller, while the valve body is located upstream, and a valve actuating means is located so that the downstream heat responding element effects an actuation of the upstream valve means. The heat responding element is located in a surface parallel with the axis of the water pump impeller.
The thermostat according to the present invention mixes bypass flow (hot coolant) and cold coolant from the radiator in the thermostat housing. The housing includes a water pump impeller, a heat responding element, and flow control valves. By utilizing a main valve and a bypass valve that are located upstream from a heat responding element, according to one embodiment, a mixing of coolants in a mixing area of the thermostat is directly controlled by the heat responding element.
The performance characteristics of the invention improve over conventional devices by making contact separately later.